So, how do we diagnose influenza?
Well, there are so many patients who
end up with influenza each flu season
that we don't run diagnostic
tests on everyone.
Typically, the diagnosis of
influenza can be made clinically,
based on the patient's history
and the physical exam findings.
If you do need to run a
diagnostic test on your patient,
there are different approaches.
They're not always indicated,
they're not always cost-effective,
and they may not help you
actually manage your patient.
So, most patients demonstrating
consistent with uncomplicated influenza
and living in an area with a local outbreak
do not require influenza testing.
So there are pros and cons to
testing, and what are these?
You've got to think about the cost.
You have to think about
the pain of the procedure,
and you have to think about the duration
and how long this test is actually
going to take to get the results.
The most commonly used test
is a nasal pharyngeal swab
called the rapid influenza test.
This test can provide results
in about 15-20 minutes.
However, the results vary, and
they're not always accurate.
Prior to testing your patient, the clinician
should assess a pre-test probability.
This will decrease the likelihood
that you have a false positive
or a false negative screening.
Here's a good diagnostic tree.
First, the clinician needs to decide,
does your patient have clinical signs
and symptoms compatible with influenza?
If it's "Yes," you can proceed
down the algorithm.
Now you have to decide,
will the results of your test change
your clinical care of your patient?
Well, they might in a patient
or a patient with a high-risk condition,
because these are the patients in
which antivirals are recommended.
You have to also think, "Will this influence
clinical practice for other patients,
such as family members or cohorting
your patients in the hospital?"
And you have to think, "Will you
initiate antiviral treatment
if clinically indicated
based on the results?"
If this doesn't change your
diagnostics, you would stop here,
but if so, you would start
your antiviral treatment
prior to the results from
your diagnostic tests.
"Yes," consider influenza
testing in your patient.
And then you're going
to interpret the results.
If your patient does not display
signs and symptoms of influenza
when they present to the clinic,
you would probably not do a
flu test on these patients.
And if you wouldn't change your treatment,
if you wouldn't need to cohort your patients,
and if it wouldn't change the
clinical care of that patient,
then also an influenza viral
testing is probably not indicated.
Here are some diagnostic options.
First, is the viral culture.
This has a moderately high sensitivity
and the highest specificity available.
It's good to confirm
influenza in your patients.
It's useful in public health surveillance,
but it's not recommended for
timely clinical management
because you won't get
these results for 2-3 days.
Another option is a PCR test.
This is the most sensitive
and specific test
that we have available
for influenza testing.
It can also be used to confirm
influenza in your patients.
It can quickly differentiate between
influenza types and subtypes,
and you'll get these
results in about 4-6 hours.
Another option in the outpatient setting
is a rapid influenza diagnostic test.
This is a screening test.
You'll get results in about 15-30 minutes.
Now, this is a good test
for ruling in influenza.
It has a very high specificity
of about 90%-95%,
but the sensitivity isn't that
great, about 50%-70%.
So you will miss influenza in
about 30%-50% of your patients.
Immunofluorescence is another option,
and this has a lower sensitivity
and specificity than the viral cell culture
and this is also a screening test.
You can get the results in 3-4 hours.
How do you manage a patient with influenza?
Well, typically, the patient will
have a self-limiting course.
They won't need anything more than
time, rest, and plenty of fluids.
A patient can take antipyretics
to bring down their fever,
but this is always an interesting
talking point with your patients.
So, what is a fever doing?
A fever is helping activate certain
immune cells that help fight the virus.
So, when a patient treats their fever,
they're actually decreasing the ability
of those immune cells to fight the virus.
So, patients are afraid of fevers.
I found that in the clinic.
I'll ask, "Why are you afraid of this fever?"
And they'll say, "Because it's- I have a fever."
And they can't really explain, and I explain
to them, the fever is helping them.
So, as long as they can stay hydrated,
as long as they can drink fluids and
tolerate their fever, they can have a fever.
It's easy for a patient to be
dehydrated when they have influenza.
They may have lost their appetite.
Maybe they're laying in their bed
sleeping for a large portion of the day.
And then also their fever, with
their increased respiratory rate,
is going to further dehydrate them.
So, encourage your patient.
They might not be hungry.
They don't need to eat for even a few days,
but they do need to keep up on their fluids.
In some cases in high-risk patients
who present early on in
their illness, antivirals,
such as Tamiflu or Relenza,
will be prescribed.
And these drugs don't really do much
once the patient is already sick.
Let's say they're going to be
sick for 10 days with influenza.
It makes it so they're going to be
sick for 9 days with influenza.
But they are less likely to die from their
influenza, if they do take the antivirals.
Now, the antivirals don't do
anything to take away the virus
that's already circulating in the body,
but they will inhibit more of
that virus from being released.
There are side effects to the medications
and patients should be
counseled about these,
and they need to weigh
the benefits and the risks.
Some common side effects
include nausea and vomiting,
and they can be lessened if
the drug is taken with food.
Now, Tamiflu has also been
associated with delirium
and self-harm behavior in teenagers.
The patient's going to need
to stay out of the community
because this is a very contagious virus,
until they're fever free for 24 hours
without needing medications
to bring it down.